Traditionally, alternating current (AC) voltage supply is controlled through mechanical relay in home automation systems application, such as applications for sprinkler valve, heating ventilating and air conditioning (HVAC), thermostat, or security camera. FIG. 1 shows a traditional HVAC control system 100 with a mechanical relay. Traditional HVAC control system 100 is coupled to an electrical grid through a transformer T1. Transformer T1 comprises a primary winding and a secondary winding. The primary winding of transformer T1 is coupled to the electrical grid to receive a first AC voltage, e.g., 110V/AC. A HVAC load 12 is coupled to the secondary winding of transformer T1 to receive a second AC voltage, e.g., 24V/AC, through a mechanical relay 11. A Micro-Controller Unit (MCU) 13 provides a command signal CMD to mechanical relay 11 to control ON/OFF of mechanical relay 11. A battery 14 is used to power MCU 13.
However, with improvement of smart home automation technology, mechanical relay is bulky and has a short and not constant operating life.